1. Field of the Invention
The present invention relates to a gas turbine load control device configured to control an amount of fuel supply to a gas turbine so as to control a gas turbine output (a power generator output) so as to achieve a target output.
2. Description of the Related Art
During a parallel-in operation of a power generator in a gas turbine power generation plant, that is, when a power generator is connected to an electric power system (an electric power network) to transmit electric power generated by the power generator to the electric power system, an amount of fuel supply to a gas turbine needs to be controlled by use of a gas turbine load control device installed in the gas turbine power generation plant so that a power generator output (active electric power) follows a variation in a requested load set value for the electric power system. The requested load set value is normally sent from a central load dispatching center to the gas turbine load control device in the form of a requested load setting command.
FIG. 11 is a block diagram showing a configuration of a conventional gas turbine load control device, and FIG. 12 is an explanatory chart showing variations of LDSET (a target output) and a power generator output (an actual output) in response to an increase in the requested load set value in a case where the gas turbine load control device is employed.
As shown in FIG. 11, the gas turbine power generation plant has a configuration in which a rotating shaft 2 of a gas turbine 1 is connected to a rotating shaft 4 of a power generator 3. Although detailed explanation will be omitted herein, the gas turbine 1 includes a gas turbine body, a compressor, and a combustor. When the gas turbine 1 starts, the power generator 3 generates electric power as the power generator 3 is driven and rotated by the gas turbine 1. The generated electric power is transmitted from the power generator 3 to an electric power system via a breaker, a transformer and other devices which are not illustrated herein. The value of the generated electric power (the active electric power) in this case is measured by a MW converter 5 serving as an active electric power meter. Then, the value (the actual output) measured by this MW converter 5 is fed back to a gas turbine load control device 10.
A fuel control valve 6 is connected to the combustor of the gas turbine 1. Gas turbine fuel, such as gas or liquid sent from an unillustrated fuel supply system such as a fuel tank, is subjected to flow rate control by the fuel control valve 6, and is then supplied to the combustor. Here, the control of opening and closing this fuel control valve 6 (the control of an amount of fuel supply) is performed by the gas turbine load control device 10. The gas turbine load control device 10 includes deviation operators (subtracters) 11 and 15, high/low monitors (comparators) 12 and 13, an analog memory 14, and a PI controller 16.
The deviation operator 11 calculates a deviation between the requested load set value (command) sent from an unillustrated central load dispatching center (a host computer) and LDSET (a load set value) equivalent to an output of the analog memory 14 (load setting deviation=requested load set value−LDSET).
The high/low monitor 12 determines whether or not the load setting deviation is equal to, or above 0.1 MW (load setting deviation≧0.1 MW). In a case where the load setting deviation is determined to be equal to, or above 0.1 MW, the high/low monitor 12 outputs a LDSET increase command to the analog memory 14. Specifically, the LDSET increase command is ON when the load setting deviation is equal to, or above 0.1 MW. The LDSET increase command is OFF when the load setting deviation is lower than 0.1 MW.
The high/low monitor 13 determines whether or not the load setting deviation is equal to, or below −0.1 MW (load setting deviation ≦−0.1 MW). In a case where the load setting deviation is determined to be equal to, or below −0.1 MW, the high/low monitor 13 outputs a LDSET decrease command to the analog memory 14. Specifically, the LDSET decrease command is ON when the load setting deviation is equal to, or below −0.1 MW. The LDSET decrease command is OFF when the load setting deviation is higher than −0.1 MW.
The analog memory 14 starts increasing the LDSET when the high/low monitor 12 inputs thereto the LDSET increase command (when the LDSET increase command is ON). The analog memory 14 gradually increases the LDSET at a predetermined pace of increase (such as 10 MW/min.) during a period when the LDSET increase command is continuously inputted (during the period when the LDSET increase command is ON). The analog memory 14 stops increasing the LDSET when the high/low monitor 12 stops inputting the LDSET increase command (when the LDSET increase command is OFF). The analog memory 14 starts decreasing the LDSET when the high/low monitor 13 inputs thereto the LDSET decrease command (when the LDSET decrease command is ON). The analog memory 14 gradually decreases the LDSET at a predetermined pace of decrease (such as −10 MW/min.) during a period when the LDSET decrease command is continuously inputted (during the period when the LDSET decrease command is ON). The analog memory 14 stops decreasing the LDSET when the high/low monitor 13 stops inputting the LDSET decrease command (when the LDSET increase command is OFF). Then, this LDSET is outputted from the analog memory 14 to the deviation operator (the subtracter) 15 as a target output.
The deviation operator 15 calculates deviation between the target output (the LDSET) set up by the analog memory 14 and the power generator output (the active electric power) measured by the MW converter 5 (output deviation=target output−power generator output).
The PI controller 16 controls an aperture of the fuel control valve 6 by performing a proportional-integral operation based on the output deviation calculated by the deviation operator 15. Specifically, when the target output is greater than the power generator output, the PI controller 16 increases the aperture of the fuel control valve 6, and thereby increases the amount of fuel supply to the gas turbine 1 (the combustor). Accordingly, the output of the gas turbine 1 is increased, and thus the output of the power generator 3 is increased (the power generator output is caused to be equal to the target output). On the other hand, when the target output is smaller than the power generator output, the PI controller 16 reduces the aperture of the fuel control valve 6, and thereby decreases the amount of fuel supply to the gas turbine 1 (the combustor). Accordingly, the output of the gas turbine 1 is decreased, and the output of the power generator 3 is decreased (the power generator output is caused to be equal to the target output). In the PI controller 16, K denotes a proportional gain; s: a Laplace operator; T: a time constant for proportional-integral control (an integral time constant); and 1/T: an integral gain.
For example, it is supposed that the requested load set value, the target output (the LDSET), and the power generator output (the actual output) are identical to one another until time T1, and that the requested load set value is increased stepwise (raised from 100 MW to 200 MW in the illustrated example) by a command from the central load dispatching center at the time T1. In this case, as shown in FIG. 12, the LDSET increase command is outputted from the high/low monitor 12 to the analog memory 14 (the LDSET increase command is ON). This is because the deviation between the requested load set value and the LDSET calculated by the deviation operator 11 is equal to, or above 0.1 MW. As a result, the analog memory 14 gradually increases the LDSET at the predetermined pace of increase from the time T1 until the LDSET reaches the requested load set value (200 MW) at time T2 (until the LDSET increase command is OFF as the load setting deviation falls below 0.1 MW). That is, the target output is gradually increased at the predetermined pace of increase.
The output deviation at this time between the target output and the power generator output (the active electric power) is calculated by the deviation operator 15, and the PI controller 16 performs the proportional-integral operation based on this output deviation. Hence, the fuel control valve 6 is activated (the valve aperture of the fuel control valve 6 is increased) on the basis of a result of this proportional-integral operation. As a consequence, the amount of fuel supply to the gas turbine 1 is increased, and the gas turbine output is increased. Accordingly, the power generator output (the active electric power) is increased. It is made possible to finally cause the power generator output (the active electric power) to be equal to the target output (the requested load set value).
The reason for gradually increasing or decreasing the LDSET (the target output) by use of the analog memory 14 is to change the LDSET (the target output) at a rate of change allowable for the gas turbine 1 even when the requested load set value is rapidly changed. When the LDSET (the target output) is rapidly changed in response to the rapid change of the requested load set value, a rapid change in the output of the gas turbine 1 may incur damage of the gas turbine 1, for example.
The documents concerning the prior art related to this application include JPA No. 10 (1998)-196315. This document discloses a method of, and a device for controlling a load on a multiple axis combined cycle plant.
In recent years, there is a growing demand from a power transmission side (the electric power system side) to the gas turbine power generation plant side that the power generator output in response to the variation in the requested load set value be caused to follow the variation faster. For example, in a country where a power generation company and a power transmission company are different from each other, there is a demand from the power transmission company to the power generation company that the power generator output in response to the variation in the requested load set value be caused to follow the variation faster.
In this regard, the conventional gas turbine load control device 10 can accelerate the follow-up of the power generator output in response to the variation in the requested load set value by setting the shorter time constant T for the proportional-integral control (i.e. by increasing the integral gain 1/T). Nevertheless, when the time constant T for the proportional-integral control is shortened, the increase and decrease of the amount of fuel supply to the gas turbine 1 is more frequently repeated as the gas turbine load control device 10 attempts to stabilize the power generator output (the active electric power) against the variation in the power generation output (the active electric power) associated with a variation in a power factor of the electric power system. Such a phenomenon is not favorable to the gas turbine 1.
For this reason, it is necessary to set the relatively long time constant T for the proportional-integral control in order to stabilize the amount of fuel supply to the gas turbine 1. However, when the long time constant T is set up for the proportional-integral control, the follow-up of the power generator output slows down at the time when the requested load set value varies. Accordingly, it is not possible to satisfy the demand from the electric power system side (the power transmission company side) that the load following capability be improved.